page_title: Sturzstrom
section_title: Movement
hierarchical_section_title: Sturzstrom / Movement
caption_attribution_description: Deutsch: Bergsturz von Köfels im Ötztal. Vor etwa 8.700 Jahren stürzten rund drei Kubikkilometer Gestein von der Westseite des Ötztals herab. Die Felsmassen blockierten den Lauf der Ötztaler Ache, die sich später eine Schlucht (Maurach) durch den Schutt fressen musste. Durch die Reibungshitze schmolz der Gneis an der Basis des Bergsturz und bildete ein glasiges Gestein, das als Köfelsit bezeichnet wird. English: Site of the Köfels landslide (Ötztal, Tyrol, Austria). About 8,700 years ago, some 3 cubic kilometers rock slided down the western side of the Ötztal. The rubble blocked the Ötztaler Ache, which later formed a small canyon (Maurach). Friction caused the Gneiss at the base of the landslide to melt, forming a glassy rock known as Köfelsite.
context_page_description: The term Sturzstrom, a German word composed of Sturz and Strom, indicates some large landslides consisting of soil and rock which travel a great horizontal distance when compared to their initial vertical drop — as much as 20 or 30 times. The term is used as a synonym to rock avalanche. Sturzstroms have similarities to the flow of glaciers, mudflows, and lava flows. They flow across land fairly easily, and their mobility increases when volume increases. They have been found on other bodies in the Solar System, including the Moon, Mars, Venus, Io, Callisto, Iapetus, and Phobos.
context_section_description: Sturzstroms may be triggered, similarly to other types of landslides, by heavy rains, earthquakes, or volcanic activity. They move rapidly, but do not necessarily require water to be present to move, and there is no definite explanation for their kinematic characteristics. One theory, the acoustic fluidization theory, hypothesizes that vibrations caused by the collisions among the rock fragments reduce friction and allow the mass to travel great distances. Another theory involves air pockets forming under the slide and providing a cushion that the slide rides over with very low friction, although the merit of this theory has been called into question by the presence of sturzstroms in vacuums such as on the Moon and Phobos. Observation of slides on Iapetus suggests that tiny contact points between bits of ice debris may heat up considerably during the movement, causing melting and forming a more fluid – and thus less friction-limited – mass of material.
  The amount of energy in a sturzstrom is much higher than in a typical landslide. Once moving, it can ride over nearly any terrain and will cover much more horizontal ground than downward-sloped ground. Its momentum can even carry the sturzstrom up small hills. The process of detachment, movement and deposition of a sturzstrom can be recorded by seismometers tens of kilometers away. The peculiar characteristics of this seismic signal make it distinguishable from that of small earthquakes. In the large Köfels landslide, which flowed into the Ötztal valley in Tyrol, Austria, deposits of fused rocks, called "frictionite" (or "impactite", or "hyalomylonite"), were found in the landslide debris. This has been hypothesized to be volcanic in origin or the result of a meteorite impact, but the leading hypothesis is that it was due to the large amount of internal friction. Friction between static and moving rocks can create enough heat to fuse rocks to form frictionite.
caption: A satellite image of the Köfels landslide showing the debris which flowed into the Ötztal valley. It is estimated that around 3 km3 of material were displaced during this slide about 9800 ± 100 years ago.[6][7]
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